Is it possible to save the planet by sticking to the speed limit? The government's transport advisors think so.

The Commission for Integrated Transport argues that emissions from cars and lorries still outweigh by some way those from air travel, though aviation is growing as a source of carbon dioxide.

One remedy, the authors conclude in a report published on Wednesday, is for us drivers to have state-sponsored lessons in eco-motoring, an idea that would cost the government little but benefit the planet a lot.

The theory is that the way you drive can be as important as what you drive, and how much you drive it.

Smooth driving

By way of an experiment, we went to the Ford test track at Dunton in Essex, to break the speed limit.

Drive at 80mph on a motorway and it is claimed your car will pump out significantly more carbon dioxide than at 70.